Method for Producing Carbon Fibers

ABSTRACT

A method for producing a carbon fiber bundle includes the acts of: providing at least one precursor, mechanically stabilizing the at least one precursor, and subsequently introducing the mechanically stabilized precursor into at least one thermal treatment device for converting the at least one precursor into at least one carbon fiber bundle. A device for producing a carbon fiber bundle has at least one oxidation furnace and a downstream carbonizing device for carbonizing a precursor to form the carbon fiber bundle, wherein a stabilizing device for mechanically stabilizing the precursor, which is introduced into the oxidation furnace, is connected upstream of the at least one oxidation furnace.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No. PCT/EP2014/056210, filed Mar. 27, 2014, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2013 206 984.7, filed Apr. 18, 2013, the entire disclosures of which are herein expressly incorporated by reference.

This application contains subject matter related to U.S. application Ser. No. ______, entitled “Method and Device for Producing Unidirectional Carbon Fibre Cloth” filed on even date herewith.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method for producing carbon fibers and to a device for the production thereof.

Carbon fibers are used to reinforce plastic components of all kinds. In particular in aviation, but also to an increasing extent in the automotive industry, this material is used in order to create particularly lightweight but nevertheless very robust components.

The carbon fibers are produced in a complex process chain. In highly simplified terms, the production process starts with the creation of what is referred to as the “precursor”, which serves as the starting material for the actual production process for the carbon fibers and usually describes a textile yarn which has a large number of individual filaments. The precursor is produced by a precursor producer and is usually wound onto transport packages after its production in order to transport the latter for further processing at a carbon fiber manufacturer.

Further processing by the carbon fiber manufacturer takes place in special production lines and includes an oxidation treatment to which the precursor is subjected. To this end, the precursor is first of all unwound from the transport packages and, subsequently, passes through a first heat treatment in a furnace (oxidation furnace) in which the precursor is alternately heated and subsequently cooled. Then, the precursor is subjected, as part of what is referred to as “carbonization”, to a second heat treatment at a temperature of between 1600 and 1900° C. in order to create a carbon fiber bundle from the precursor by chemical transformation.

Usually, during the production of the precursor, what is referred to as “entanglement” is carried out, that is to say the individual filaments of the precursor are entangled. In this case, the generally highly parallel orientation of the individual filaments to one another is “entangled” in a targeted manner in order to mechanically stabilize the precursor for better processability. The degree of entanglement of the individual filaments has a great influence on stable processability during the production of the carbon fibers and thus represents an important influencing variable for the carbon fibers and the products produced therefrom.

For this reason, great efforts are made to retain the mechanical stabilization to the greatest possible extent in spite of repeated deflection of the precursor during production and during subsequent winding onto the transport packages, and during packing and transport from the precursor producer to the carbon fiber manufacturer. The aim is not to eliminate the effect of mechanical stabilization but to allow stable processability during the production of the carbon fibers.

The same goes for the subsequent unwinding and feeding into the carbonization process in order to produce the carbon fiber bundles from the unwound precursor.

Process parameters of the precursor producer and the mechanical load during said processing steps play a particularly decisive role in the degree of remaining mechanical stabilization during introduction into the carbonization process.

It is therefore the object of the invention to simplify the process of carbon fiber production and to improve mechanical stabilization of the precursor.

This and other objects are achieved by way of a method and a device according to embodiments of the invention.

Accordingly, a method is proposed for producing a carbon fiber bundle, having the following steps:

-   -   a) provision of at least one precursor,     -   b) mechanical stabilization of the at least one precursor, and     -   c) subsequent introduction of the mechanically stabilized         precursor into at least one heat treatment device in order to         convert the at least one precursor into at least one carbon         fiber bundle.

One or more precursors are thus first of all mechanically stabilized and fed to one or more heat treatment devices. This should be understood as meaning that these two steps are carried out one after the other, that is to say successively within one and the same production line. In this way, it is possible to ensure that the precursor is introduced into the heat treatment device in a sufficiently mechanically stabilized manner and has thus been prepared for subsequent carbonization.

A particular advantage has been found to be that the precursor can be adapted individually to the subsequent processing by the combination of steps of mechanical stabilization and subsequent introduction. It is therefore possible, independently of any pretreatment of the precursor that has been carried out during the production thereof, to adapt the mechanical stabilization conditions in an appropriate manner and optionally to vary them such that adaptive control and targeted adaptation is possible with regard to subsequent process and product properties. It is thus possible to dispense with mechanical stabilization during the production of the precursor or stabilization that has already been carried out during said production can be subsequently adapted and improved.

Heat treatment devices should be understood as being, for example, one or more oxidation furnaces for oxidizing the precursor and/or at least one carbonizing device for carbonizing the precursor.

According to one embodiment, the provision act includes unwinding of the at least one precursor from at least one package. In other words, the precursor is thus provided on a package for the method and subsequently unwound therefrom and subjected to the subsequent stabilization step before the precursor is oxidized in the oxidation furnace or carbonized in the carbonizing device.

Preferably, the mechanical stabilization act can take place immediately before the subsequent introduction into the at least one heat treatment device. The term “immediately” should be understood as being a sequence of steps that follow one another directly in space and time, and so no significant intermediate steps for treating the precursor are provided. Of course, this does not rule out intermediate changes in direction of the precursor.

In accordance with a further embodiment, the mechanical stabilization act can include entangling of individual filaments of the precursor. As a result of the individual filaments being entangled, for example by way of an air jet, it is possible—as already illustrated above—to change the properties of the precursor. In particular, the entanglement allows more stable processability during the production of the carbon fiber bundles than is the case for non-entangled individual filaments of the precursor. In addition, more uniform processability of the carbon fiber bundle produced arises in the context of textile further processing, and improved injection behavior for the injection of a matrix.

Thus, by means of the described method, the subsequent properties of the carbon fiber bundle produced can be influenced in a decisive and targeted manner shortly before the introduction into the oxidation furnace.

Furthermore, a device for producing a carbon fiber bundle is provided, the device including:

-   -   at least one oxidation furnace; and     -   a downstream carbonizing device for carbonizing a precursor to         form the carbon fiber bundle,     -   wherein a stabilizing device for mechanically stabilizing the         precursor introduced into the oxidation furnace is connected         upstream of the at least one oxidation furnace.

The device thus represents at least a part of a production line by way of which the above-described method can be carried out and in this way—as explained above—the subsequent properties of the carbon fiber bundle produced can be influenced in a targeted manner.

For example, the stabilizing device can be arranged immediately upstream of the at least one oxidation furnace (with respect to a conveying direction of the device). The stabilizing device is thus positioned in the direct spatial vicinity of the oxidation furnace, and so a sequence of steps that follow one another directly in time without further intermediate steps is enabled. Of course, interposed changes in direction are not ruled out thereby.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of a carbon fiber bundle producing device according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic illustration of a device 10 for producing a carbon fiber bundle 11, having two heat treatment devices 12, 13 in the form of an oxidation furnace 12 and a subsequent carbonizing device 13 for carbonizing a precursor 14 to form a carbon fiber bundle 11. In the embodiment illustrated, the precursor 14 is provided on a package 15 and is unwound therefrom.

A stabilizing device 16 for mechanically stabilizing the precursor 14 introduced into the oxidation furnace 12 is connected upstream of the oxidation furnace 12 such that the stabilizing device 16 is arranged immediately upstream of the oxidation furnace 12 (and thus following the provision of the precursor 14).

It is thus possible to mechanically stabilize the precursor 14 immediately before the subsequent introduction of the precursor 14 and, thus, to adapt the latter individually to the subsequent processing.

Of course, the device 10 for producing the carbon fiber bundle 11 can have further components (not illustrated), in particular for further processing of the carbon fiber bundles 11 that are produced.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

What is claimed is:
 1. A method for producing a carbon fiber bundle, the method comprising the acts of: a) providing at least one precursor; b) mechanically stabilizing the at least one precursor; and c) subsequently introducing the mechanically stabilized precursor into at least one heat treatment device in order to convert the at least one precursor into at least one carbon fiber bundle.
 2. The method according to claim 1, wherein the providing act comprises the act of unwinding the at least one precursor from at least one package.
 3. The method according to claim 1, wherein the mechanically stabilizing act takes place immediately before the subsequent introduction into the at least one heat treatment device.
 4. The method according to claim 2, wherein the mechanically stabilizing act takes place immediately before the subsequent introduction into the at least one heat treatment device.
 5. The method according to claim 1, wherein the mechanically stabilizing act comprises the act of entangling individual filaments of the precursor.
 6. The method according to claim 4, wherein the mechanically stabilizing act comprises the act of entangling individual filaments of the precursor.
 7. A device for producing a carbon fiber bundle, comprising: at least one oxidation furnace; a downstream carbonizing device for carbonizing a precursor to form the carbon fiber bundle; and a stabilizing device for mechanically stabilizing the precursor introduced into the oxidation furnace, the stabilizing device being connected upstream of the at least one oxidation furnace.
 8. The device according to claim 7, wherein the stabilizing device is arranged immediately upstream of the at least one oxidation furnace. 